1. Field of the Invention
The present invention relates to a damper, and more particularly to a magnetic-rheological fluid damper.
2. Discussion of the Related Art
During the past decade there has been increasing interest in the development of controllable dampers that utilize electro-rheological fluids (ERF) and magneto-rheological fluids (MRF). The possibility of using ERF or MRF based damping devices in various applications has made these controllable devices attractive to the vibration control field. Controllable dampers can potentially be used in a variety of mechanical systems such as bicycles, motorcycles, automobiles, trucks, ships, trains, airplanes, bridges, buildings, sports equipment and any other systems in which passive, or semi-active vibration control is useful.
Magneto-rheological fluid generally consists of micron-sized particles suspended in a carrier fluid,,such as silicon or mineral oils. The particles are ferrous in nature, and therefore become polarized in the presence of a magnetic field. The polarization of the particles results in a magnetic attraction, causing the particles to form chains (or columns) dependent upon field strength. These chains align with the magnetic field lines. The chains of particles in the MRF induce changes in the physical properties of the fluid. One change is an appreciable increase (or decrease) in the yielded stress and the plastic viscosity of the MRF because the chains resist flow. MRF is capable of responding to a change in its magnetic field within a few milliseconds and retains no residual charge.
To produce and control the change in the material properties of MRF, electromagnets and/or permanent magnets are used in conjunction with the housing that contains the fluid. By varying electric current passing through the electromagnet, intensity and strength of the magnetic field can be controlled. The strength of the magnetic field that passes through the region of MRF determines the level of change of the MRF""s yielded stress and plastic viscosity. When MRF is used as a replacement for hydraulic fluid in dampers, the varying yielded stress and plastic viscosity produces a varying damping force. The end result is a controllable damper.
One of the most popular applications for controllable dampers is in automobiles, trucks, and other vehicles equipped with shock absorbers. These vehicles have sensors and on-board computers (in varying levels of complexity) that are capable of sensing and actively responding to random excitation inputs such as rough roads, bumps, changes in vehicle mass, etc. Vehicles equipped with active or semi-active suspension systems generally provide increased safety, have improved. vehicle-handling characteristics, and provide a smoother, more comfortable ride.
There are several benefits to MRF controllable dampers as compared to mechanically controlled hydraulic dampers. Mechanically controlled dampers have internal valves and other moving parts that are exposed to great forces and often fail in operation. MRF dampers require no moving internal parts to control damping, thereby reducing the mechanical complexity and cost of the device. An MRF damper is a controllable damper with a fast response time that benefits from a simple, rapid change in material properties of the fluid. The hydraulic fluid components of a mechanically controlled damper are also sensitive to the introduction of impurities. Vehicle dampers are often externally exposed to impurities. MRF dampers are insensitive to the introduction of impurities.
However, current MRF controllable dampers suffer from a number of limitations and undesirable characteristics. Specifically, a magnetic field must be applied to the passage through which the MRF flows. As a result of the magnetic requirements of MRF dampers, ferrous materials have almost been exclusively used in their construction. These ferrous materials provide magnetic pathways for the magnetic fields. However, ferrous materials are relatively heavy in weight. MRF dampers have been typically too heavy for weight-sensitive applications such as fighter aircraft landing gear, racing cars, mountain bicycles, etc. Also, conventional MRF dampers have restrictively small dimensional tolerances in the regions where the magnetic field is applied to the MRF. As a result of the tolerance restrictions, manufacturing methods are difficult and expensive. This type of MRF damper is also sensitive to off-axis loading, as bending and buckling loads affect the tolerance regions. In addition, due to the ferrous particles in the fluid, the fluid is abrasive and affects the same tolerance-sensitive regions, thereby possibly resulting in shorter life span, high-maintenance MRF dampers.
Accordingly, the present invention is directed to an MRF damper that substantially obviates one or more of the problems due do limitations and disadvantages of the related art.
An object of the present invention is to provide a controllable MRF damper having increased damping.
Another object of the present invention is to provide an MRF damper that can be easily manufactured at a low cost.
Another object of the present invention is to provide an MRF that does not require restrictive dimensional tolerances.
Another object of the present invention is to provide an MRF damper that does not necessarily require the use of ferrous materials.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a magneto-rheological fluid device includes a housing
defining a cavity; a piston slidably disposed in the cavity, the piston dividing the cavity into first and second portions; a passage defined on an exterior surface of the piston fluidly coupling the first and second portions of the cavity; a magneto-rheological fluid disposed in the cavity such that motion of the piston is damped by flow of the magneto-rheological fluid through the passage; and a magnet disposed to produce a magnetic field within the cavity substantially parallel to the motion of the piston at the exterior surface of the piston.
In another aspect, a magneto-rheological fluid device includes a housing defining a cavity; a piston slidably disposed in the cavity, the piston dividing the cavity into first and second portions; a passage defined on the piston fluidly coupling the first and second portions of the cavity, the passage having a transverse portion formed along a circumference of the piston; a magneto-rheological fluid disposed in the cavity such that motion of the piston is damped by flow of the magneto-rheological fluid through the passage; and a magnet disposed to produce a magnetic field within the cavity.
In another aspect, a magneto-rheological fluid device includes a housing defining a cavity; a piston slidably disposed in the cavity, the piston dividing the cavity into first and second portions; a passage defined on the piston fluidly coupling the first and second portions of the cavity; a magneto-rheological fluid disposed in the cavity such that motion of the piston is damped by flow of the magneto-rheological fluid through the passage; and a magnet disposed around the housing to produce a magnetic field within the cavity substantially parallel to the motion of the piston at the exterior surface of the piston.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.